Does menace require both blockers to be declared at the same time or can they be assigned separately?

Menace requires that a creature with menace be blocked by two or more creatures if it is blocked at all. This restriction applies at the moment blockers are declared — specifically during the Declare Blockers Step (CR 509.1). All blocking creatures are declared simultaneously in that single step, not one at a time across different phases or steps.

CR 702.111b states: 'A creature with menace can't be blocked except by two or more creatures.' The legality of each block assignment is checked after all blockers are declared (CR 509.2). If fewer than two creatures are assigned to block a creature with menace, that block is illegal and must be corrected before the game proceeds.

There is no mechanism that allows a defending player to 'add' a second blocker after the declare blockers step has concluded. Once blockers are declared and the step moves forward, blocking assignments are locked in. You cannot, for example, declare one blocker and then wait to see what happens before committing a second.

Concrete example: Your opponent attacks with a 3/3 with menace. During your Declare Blockers Step, you must assign at least two of your creatures to block it all at once — say a 2/2 and a 1/1 simultaneously. You cannot declare just the 2/2 as a blocker first and then later add the 1/1; if you only declare one blocker for that creature, the block is illegal.

In summary, the two-or-more-blocker requirement of menace is evaluated at the end of the declare blockers step (CR 509.2), meaning both blockers must be part of the same simultaneous declaration.